UK: IMechE recommends rail electrification instead of hydrogen trains

9 February 2019

The Institution of Mechanical Engineers (IMechE) released a report titled “The Future for Hydrogen Trains in the UK”, which encourages greater electrification of the UK national train network—as opposed to hydrogen powered trains—as the most effective strategy to decarbonize UK rail transport.

The IMechE report contradicts the rail policy by the UK Government. In February 2018, the UK Minister for Transport, Jo Johnson, proposed to “phase out” all British diesel locomotives by 2040. This ambitious task—as diesel accounts for about a third of all Britain’s trains—would be achieved through such technologies as battery powered and hydrogen fuel cell locomotives, rather than electrification. UK Network Rail’s electrification plans, including the Welsh and Midlands mainlines, were postponed or abandoned by Johnson’s ministerial predecessor.

Typical efficiencies for electrolysis (to produce low-carbon H2) and fuel cells are respectively 68% and 52%, IMechE said in the report. Compressing hydrogen for storage, typically at 350 bar, requires 6% of its chemical energy. The overall cycle efficiency from multiplying all these efficiencies is 33%. Hence hydrogen traction requires 3 kW of electricity to deliver 1 kW of power to the wheel. An electric train has no on-board energy conversion, so needs only 1.2 kW.

This low overall cycle efficiency potentially undermines the green credentials of hydrogen trains, as they require 2.5 times the electrical energy of a comparable electric train. Hydrogen trains could be more viable if new energy technologies were implemented—for instance using otherwise surplus overnight (e.g., wind-turbine) generating capacity to produce and store hydrogen.

A further constraint is hydrogen’s low energy density. At 350 bar, the volumetric energy density of hydrogen is 4.6 MJ/L, compared with 35.8 MJ/L for diesel. So a hydrogen train requires fuel storage eight times the size of a diesel train’s fuel tank. For this reason, high-powered, long-range hydrogen traction would require addition vehicles with hydrogen tanks, which would reduce the number of passengers or freight on the train.

The IMechE recommended that the UK Government rethinks the cancellation of electrification programs and moves forward with a more innovative, and long-term approach electrification rolling program.

The report also recommends that the industry encourages the development and deployment of hydrogen trains and their fuelling and servicing facilities. Creating and supporting demonstration lines and trains will help to de-risk the technologies. H2 train technology should be developed in industrial areas where hydrogen production already occurs—from either petrochemical industries or using renewable energy supplies for electrolysis—and can support the wider transport system.